Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Modulation of Fibrillogenesis of Amyloid β(1−40) Peptide with Cationic Gemini Surfactant

Modulation of the fibrillogenesis of amyloid peptide Aβ(1−40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) has been studied. Both UV−vis and AFM results show that C12C6C12Br2 monomers can promote the fibrillogenesis of Aβ(1−40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Aβ(1−40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Aβ(1−40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Aβ(1−40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the α-helix to β-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Aβ(1−40) aggregates also vary upon increasing C12C6C12Br2 concentration

Aggregation Behavior of Nitrophenoxy-Tailed Quaternary Ammonium Surfactants

Cationic surfactants N,N,N-trimethyl-10-(4-nitrophenoxy)decylammonium bromide (N10TAB) and N,N,N‘,N‘-tetramethyl-N,N‘-bis[10-(4-nitrophenoxy)decyl]-1,6-hexanediammonium dibromide (N10-6-10N), bearing aromatic nitrophenoxy groups in the ends of their hydrophobic chains, have been synthesized, and their self-assembling properties in aqueous solutions have been studied by conductivity, isothermal titration microcalorimetry, 1H NMR spectroscopy, and dynamic light scattering. Below the critical micelle concentration, N10-6-10N can form premicelles with 2 or 3 surfactant molecules. Beyond the critical micelle concentration, the two surfactants have strong self-aggregation ability and can form micelles of rather small size and with small aggregation numbers N, which are 30 ± 3 for N10TAB and 20 ± 2 for N10-6-10N, respectively. Also, the variations in 1H NMR signals at different surfactant concentrations provide the information on the environmental change of the surfactants upon their micellization progress. The most prominent phenomenon is the shielding effect of the aromatic groups over the protons in the aliphatic chains, implying that the nitrophenoxy groups partially insert into the micelles and face the several middle methylenes of the hydrophobic side chains

Self-Assembly of Oleyl Bis(2-hydroxyethyl)methyl Ammonium Bromide with Sodium Dodecyl Sulfate and Their Interactions with Zein

Surface tension and aggregation behavior in an aqueous solution of the mixture of cationic surfactant oleyl bis­(2-hydroxyethyl)­methylammonium bromide (OHAB) and anionic surfactant sodium dodecyl sulfate (SDS) have been studied by surface tension, conductivity, turbidity, zeta potential, isothermal titration microcalorimetry (ITC), cryogenic transmission electron microscopy (Cryo-TEM), and dynamic light scattering. The mixture shows pretty low critical micellar concentration and surface tension, and successively forms globular micelles, unilamellar vesicles, multilamellar vesicles, rod-like micelles, and globular micelles again by increasing the molar fraction of OHAB from 0 to 1.00. The cooperation of hydrophobic interaction between the alkyl chains, electrostatic attraction between the headgroups as well as hydrogen bonds between the hydroxyethyl groups leads to the abundant aggregation behaviors. Furthermore, the solubilization of zein by the OHAB/SDS aggregates and their interactions were studied by ITC, total organic carbon analysis (TOC), and Cryo-TEM. Compared with pure OHAB or pure SDS solution, the amount of zein solubilized by the OHAB/SDS mixture is significantly reduced. It means that the mixtures have much stronger abilities in solubilizing zein. This result has also been proved by the observed enthalpy changes for the interaction of OHAB/SDS mixture with zein. Mixing oppositely charged OHAB and SDS reduces the net charge of mixed aggregates, and thus, the electrostatic attraction between the aggregates and zein is weakened. Meanwhile, the large size of the aggregates may increase the steric repulsion to the zein backbone. This work reveals that surfactant mixtures with larger aggregates and smaller CMCs solubilize less zein, suggesting how to construct a highly efficient and nonirritant surfactant system for practical use

Complex Formation and Aggregate Transitions of Sodium Dodecyl Sulfate with an Oligomeric Connecting Molecule in Aqueous Solution

Anionic single-tail surfactant sodium dodecyl sulfate (SDS) and a molecule with multiple amido and amine groups (Lys-12-Lys) were used as building blocks to fabricate oligomeric surfactants through intermolecular interactions. Their interactions and the resultant complex and aggregate structures were investigated by turbidity titration, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, freeze-fracture transmission electron microscopy, ¹H NMR, and 1D NOE techniques. At pH 11.0, the interaction between SDS and Lys-12-Lys is exothermic and mainly resulted from hydrogen bonding among the amido and amine groups of Lys-12-Lys and the sulfate group of SDS and hydrophobic interaction between the hydrocarbon chains of SDS and Lys-12-Lys. At pH 3.0, each Lys-12-Lys carries four positive charges and two hydrogen bonding sites. Then SDS and Lys-12-Lys form complexes Lys-12-Lys­(SDS)₆ and Lys-12-Lys­(SDS)₄ through the head groups by electrostatic attraction and hydrogen bonds assisted by hydrophobic interaction. Moreover, the complexes pack more tightly in their aggregates with the increase of the molar ratio. Especially the Lys-12-Lys­(SDS)₄ and Lys-12-Lys­(SDS)₆ complexes behave like oligomeric surfactants taking Lys-12-Lys as a spacer group, exhibiting a series of aggregates transitions with the increase of concentration, i.e., larger vesicles, smaller spherical micelles, and long threadlike micelles. Therefore, oligomeric surfactants Lys-12-Lys­(SDS)₄ and Lys-12-Lys­(SDS)₆ have been successfully fabricated by using a single chain surfactant and an oligomeric connecting molecule through noncovalent association

Aggregation Behavior of a Tetrameric Cationic Surfactant in Aqueous Solution

A star-shaped tetrameric quaternary ammonium surfactant PATC, which has four hydrophobic chains and charged hydrophilic headgroups connected by amide-type spacer group, has been synthesized in this work. Surface tension, electrical conductivity, ITC, DLS, and NMR have been used to investigate the relationship between its chemical structure and its aggregation properties. Interestingly, a large size distribution around 75 nm is observed below the critical micelle concentration (cmc) of PATC, and the large size distribution starts to decrease beyond the cmc and finally transfers to a small size distribution. It is proved that the large size premicellar aggregates may display network-like structure, and the size decrease beyond the cmc is the transition of the network-like aggregates to micelles. The possible reason is that intramolecular electrostatic repulsion among the charged headgroups below the cmc leads to a star-shaped molecular configuration, which may form the network-like aggregates through intermolecular hydrophobic interaction between hydrocarbon chains, while the hydrophobic effect becomes strong enough to turn the molecular configuration into pyramid-like shape beyond the cmc, which make the transition of network-like aggregates to micelles available

Disaggregation Ability of Different Chelating Molecules on Copper Ion-Triggered Amyloid Fibers

Dysfunctional interaction of amyloid-β (Aβ) with excess metal ions is proved to be related to the etiology of Alzheimer’s disease (AD). Using metal-binding compounds to reverse metal-triggered Aβ aggregation has become one of the potential therapies for AD. In this study, the ability of a carboxylic acid gemini surfactant (SDUC), a widely used metal chelator (EDTA), and an antifungal drug clioquinol (CQ) in reversing the Cu²⁺-triggered Aβ(1–40) fibers have been systematically studied by using turbidity essay, BCA essay, atomic force microscopy, transmission electron microscopy, and isothermal titration microcalorimetry. The results show that the binding affinity of Cu²⁺ with CQ, SDUC, and EDTA is in the order of CQ > EDTA > SDUC, while the disaggregation ability to Cu²⁺-triggered Aβ(1–40) fibers is in the order of CQ > SDUC > EDTA. Therefore, the disaggregation ability of chelators to the Aβ(1–40) fibers does not only depend on the binding affinity of the chelators with Cu²⁺. Strong self-assembly ability of SDUC and π–π interaction of the conjugate group of CQ also contributes toward the disaggregation of the Cu²⁺-triggered Aβ(1–40) fibers and result in the formation of mixed small aggregates

Self-Assembly of Aβ-Based Peptide Amphiphiles with Double Hydrophobic Chains

Two peptide–amphiphiles (PAs), 2C₁₂–Lys–Aβ­(12–17) and C₁₂–Aβ­(11–17)–C₁₂, were constructed with two alkyl chains attached to a key fragment of amyloid β-peptide (Aβ(11–17)) at different positions. The two alkyl chains of 2C₁₂–Lys–Aβ­(12–17) were attached to the same terminus of Aβ(12–17), while the two alkyl chains of C₁₂–Aβ­(11–17)–C₁₂ were separately attached to each terminus of Aβ(11–17). The self-assembly behavior of both the PAs in aqueous solutions was studied at 25 °C and at pHs 3.0, 4.5, 8.5, and 11.0, focusing on the effects of the attached positions of hydrophobic chains to Aβ(11–17) and the net charge quantity of the Aβ(11–17) headgroup. Cryogenic transmission electron microscopy and atomic force microscopy show that 2C₁₂–Lys–Aβ­(12–17) self-assembles into long stable fibrils over the entire pH range, while C₁₂–Aβ­(11–17)–C₁₂ forms short twisted ribbons and lamellae by adjusting pHs. The above fibrils, ribbons, and lamellae are generated by the lateral association of nanofibrils. Circular dichroism spectroscopy suggests the formation of β-sheet structure with twist and disorder to different extents in the aggregates of both the PAs. Some of the C₁₂–Aβ­(11–17)–C₁₂ molecules adopt turn conformation with the weakly charged peptide sequence, and the Fourier transform infrared spectroscopy indicates that the turn content increases with the pH increase. This work provides additional basis for the manipulations of the PA’s nanostructures and will lead to the development of tunable nanostructure materials

Aggregation Behavior of Sodium Lauryl Ether Sulfate with a Positively Bicharged Organic Salt and Effects of the Mixture on Fluorescent Properties of Conjugated Polyelectrolytes

The aggregation behavior of anionic single-chain surfactant sodium lauryl ether sulfate containing three ether groups (SLE3S) with positively bicharged organic salt 1,2-bis­(2-benzylammoniumethoxy)­ethane dichloride (BEO) has been investigated in aqueous solution, and the effects of the BEO/SLE3S aggregate transitions on the fluorescent properties of anionic conjugated polyelectrolyte MPS-PPV with a larger molecular weight and cationic conjugated oligoelectrolyte DAB have been evaluated. Without BEO, SLE3S does not affect the fluorescent properties of MPS-PPV and only affects the fluorescent properties of DAB at a higher SLE3S concentration. With the addition of BEO, SLE3S and BEO form gemini-like surfactant (SLE3S)₂-BEO. When the BEO/SLE3S molar ratio is fixed at 0.25, with increasing the BEO/SLE3S concentration, the BEO/SLE3S mixture forms large, loosely arranged aggregates and then transforms to closely packed spherical aggregates and finally to long thread-like micelles. The photoluminescence (PL) intensity of MPS-PPV varies with the morphologies of the BEO/SLE3S aggregates, while the PL intensity of DAB is almost independent of the aggregate morphologies. The results demonstrate that gemini-like surfactants formed through intermolecular interactions can effectively adjust the fluorescent properties of conjugated polyelectrolytes